The invention relates generally to an ignition system for use in combustion engines having multiple fuel capabilities.
Direct fuel injected engines combusting low cetane/high octane fuels typically utilize high compression ratios and unthrottled conditions to achieve efficient operation. Late fuel injection during the combustion cycle is also used to avoid knocking at the high compression ratios. A problem with the late injection engines, however, is that the resulting stratified charge and lean air mixtures result in incomplete combustion and high emission levels.
An approach to provide satisfactory combustion of the stratified charge is to ignite the charge with a conventional spark plug operating with high ignition power. A disadvantage of this approach is that the high ignition power drastically reduces the spark plug life.
Another approach is to ignite a small air/fuel charge in a prechamber which requires low levels of ignition power and then to direct the ignited charge into the combustion chamber. Examples of this approach are disclosed in U.S. Pat. Nos. 4,019,473 and 4,342,300.
Still another approach is to position a grid of catalytic material within the combustion chamber such as, for example, disclosed in U.S. Pat. Nos. 4,092,967 and 4,480,613. The complexity of such a system, however, is undesirable.